adding xt::adapt(xt::sequence_view).

[vakokako]

Usually when working with tensor shapes, we use xt::adapt. This works great, since shapes are always containers, except when using xt::view with xt::all() in all dimensions, the shape returned will be xt::sequence_view, which you cannot adapt correctly.
So this pull request allows the following:

auto shape = xt::adapt(xt::view(tensor, xt::all()).shape());

[JohanMabille]

What error do you have when you class xt::adapt with an xt::sequence_view object? I would expect the compiler to select this overload.

[vakokako]

[build] In file included from ../main.cpp:5:
[build] In file included from /home/code/vcpkg/installed/x64-linux/include/xtensor/xadapt.hpp:20:
[build] In file included from /home/code/vcpkg/installed/x64-linux/include/xtensor/xarray.hpp:20:
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xcontainer.hpp:47:38: error: no type named 'allocator_type' in 'xt::sequence_view<std::array<unsigned long, 2>, 0, 2>'
[build]             using type = typename T::allocator_type;
[build]                          ~~~~~~~~~~~~^~~~~~~~~~~~~~
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xcontainer.hpp:58:5: note: in instantiation of template class 'xt::detail::allocator_type_impl<xt::sequence_view<std::array<unsigned long, 2>, 0, 2>>' requested here
[build]     using allocator_type_t = typename detail::allocator_type_impl<T>::type;
[build]     ^
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xcontainer.hpp:81:32: note: in instantiation of template type alias 'allocator_type_t' requested here
[build]         using allocator_type = allocator_type_t<std::decay_t<storage_type>>;
[build]                                ^
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xcontainer.hpp:257:39: note: in instantiation of template class 'xt::xcontainer<xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>>' requested here
[build]     class xstrided_container : public xcontainer<D>
[build]                                       ^
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xtensor.hpp:209:36: note: in instantiation of template class 'xt::xstrided_container<xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>>' requested here
[build]     class xtensor_adaptor : public xstrided_container<xtensor_adaptor<EC, N, L, Tag>>,
[build]                                    ^
[build] ../main.cpp:64:27: note: in instantiation of template class 'xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>' requested here
[build]     auto sequence_adapt = xt::adapt(xt::view(tensor, xt::all(), xt::all()).shape());
[build]                           ^
[build] In file included from ../main.cpp:5:
[build] In file included from /home/code/vcpkg/installed/x64-linux/include/xtensor/xadapt.hpp:21:
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xtensor.hpp:222:52: error: no type named 'allocator_type' in 'xt::xstrided_container<xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>>'
[build]         using allocator_type = typename base_type::allocator_type;
[build]                                ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
[build] ../main.cpp:64:27: note: in instantiation of template class 'xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>' requested here
[build]     auto sequence_adapt = xt::adapt(xt::view(tensor, xt::all(), xt::all()).shape());
[build]                           ^
[build] In file included from ../main.cpp:5:
[build] In file included from /home/code/vcpkg/installed/x64-linux/include/xtensor/xadapt.hpp:21:
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xtensor.hpp:225:54: error: no type named 'backstrides_type' in 'xt::xstrided_container<xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>>'
[build]         using backstrides_type = typename base_type::backstrides_type;
[build]                                  ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xtensor.hpp:592:11: error: type 'xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>::base_type' (aka 'xstrided_container<xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1UL, (xt::layout_type)1, xt::xtensor_expression_tag>>') is not a direct or virtual base of 'xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>'
[build]         : base_type(), m_storage(std::forward<D>(storage))
[build]           ^~~~~~~~~
[build] /home/code/vcpkg/installed/x64-linux/include/xtensor/xadapt.hpp:218:16: note: in instantiation of function template specialization 'xt::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &, 1, xt::layout_type::row_major, xt::xtensor_expression_tag>::xtensor_adaptor<const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &>' requested here
[build]         return return_type(std::forward<C>(container), shape, l);
[build]                ^
[build] ../main.cpp:64:31: note: in instantiation of function template specialization 'xt::adapt<xt::layout_type::row_major, const xt::sequence_view<std::array<unsigned long, 2>, 0, 2> &>' requested here
[build]     auto sequence_adapt = xt::adapt(xt::view(tensor, xt::all(), xt::all()).shape());
[build]                               ^

[JohanMabille]

Sorry for the late reply, I think it would be better to add an allocator_type type in xsequence_view rather than adding a specific overload. The allocator_type can be that of the underying expression E.